1. Field of the Invention
The present invention relates to a frictional resistance generation mechanism. More specifically, the present invention relates to a mechanism for attenuating torsional vibration that is disposed between two relatively rotatable members of a rotating mechanism, and is designed to generate frictional resistance and to attenuate the torsional vibration due to the torsional friction when the two members rotate relative to each other.
2. Background Information
A clutch disk assembly used in vehicles has a clutch function for engaging or disengaging a flywheel, and a damper function for absorbing and attenuating torsional vibration from the flywheel. A vehicle commonly emits abnormal, i.e. deviating from a standard, noises during idling (rattling noise), abnormal noises while running (acceleration/deceleration rattling, booming noise), and tip-in/tip-out noise (low frequency vibration). It is a function of the damper of the clutch disk assembly to eliminate these abnormal noises and vibrations.
An abnormal noise while idling is a noise that can be heard as a “rattle” generated by the transmission when shifted into the neutral gear and the clutch pedal is released while waiting at a traffic light or the like. The reason for this abnormal noise is that the engine torque is low in the vicinity of engine idling rotation, and torque fluctuation is considerable during engine firing. Rattling noise occurs between the counter gear and input gear of the transmission at this time.
The tip-in/tip-out (low frequency vibration) refers to the considerable longitudinal lurch of the car body that is generated when the accelerator pedal is suddenly depressed or released. When the rigidity of the drive transmission system is low, the torque transmitted to the tires is conversely transmitted to the drive transmission system from the tires, and excessive torque is generated in the tires as a backlash. The result is a longitudinal vibration that violently and transiently shakes the car body in the longitudinal direction.
The torsion characteristics of a conventional clutch disk assembly are insufficient in the vicinity of the zero torque to counter the abnormal noise during idling because the torsional rigidity at this point should be low. On the other hand, the torsion characteristics of the clutch disk assembly body must be as solid or rigid as possible to counter the longitudinal vibrations of tip-in/tip-out.
To solve the above-described problems, a clutch disk assembly in which a two-stage characteristic is realized by using two types of spring members is provided. In view of the above, this has an effect of preventing abnormal noise during idling because the torsional rigidity and the hysteresis torque are kept low in the first stage (low torsional angle area) in the torsion characteristics. The longitudinal vibration of tip-in/tip-out can be sufficiently attenuated because the torsional rigidity and the hysteresis torque are set high in the second stage (high torsional angle area) in the torsion characteristics. Also known is a damper mechanism for efficiently absorbing minute torsional vibrations by not allowing the large friction mechanism in the second stage to operate when minute torsional vibrations, which are caused, for example, by combustion fluctuations in the engine in the second stage of torsion characteristics, are inputted.
The entire frictional resistance generation mechanism in the above-described damper mechanism is arranged to act parallel to the direction of rotation with a highly rigid spring member, and further has a frictional resistance generating unit and a rotational direction coupling that is disposed so as to act parallel to the direction of rotation in relation thereto. The rotational direction coupling has a narrow rotational direction gap between two members. Therefore, there is no collision in the rotational direction coupling when minute torsional vibrations caused by combustion fluctuations in the engine are inputted. Further, at this time, the frictional resistance generating unit does not operate.
On the other hand, the frictional unit operates in response to torsional vibrations with a large torsional angle. The frictional resistance generating unit does not operate in the narrow rotational direction gap at both ends of the torsional angle. That is to say, when a torsional vibration with a large torsional angle is input, a sudden shift occurs from the area where the frictional resistance generating unit does not operate to the area of large frictional resistance in which the frictional resistance generating unit does operate at both ends of the torsional angle. In other words, the impact is considerable when the members including the gap in the rotational direction collide with each other because large frictional resistance builds up in the vertical direction. As a result, a so-called knocking sound is generated.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved frictional resistance generation mechanism. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.